Carbon materials have low specific gravity and excellent heat resistance, corrosion resistance, slidability, electrical conductivity, heat conductivity, and workability, and are therefore conventionally used in a wide variety of fields including semiconductor technology, metallurgy, mechanical technology, electrotechnology, and nuclear technology.
However, carbon materials generally have a problem in that they are poor in oxidation resistance and strength. To solve this problem, it has been considered to combine a carbon material and another material, such as ceramics, into a composite.
Examples of the combination of a carbon material and a ceramic material into a composite include SiC-coated graphite composite materials in which a graphite base material is coated with SiC or TaC by a vapor phase reaction or a melt reaction, and the SiC-coated graphite composite materials are utilized as susceptors for producing compound semiconductors by chemical vapor deposition. Although these products have heat resistance and chemical stability and prevent dust generation from graphite particles, they do not provide increased strength and their production cost is high. Therefore, the products are limited to some applications, such as a susceptor. In addition, it is technically difficult to provide uniform coating on graphite base materials having three-dimensionally complex shapes.
Meanwhile, an SiC/carbon composite material has been developed in which porous carbon is impregnated with molten silicon at a high temperature to induce a combustion synthesis reaction and the insides of pores in the porous carbon are thereby converted to SiC (see Patent Literature 1). For this composite material, a near-net-shape product can be formed based on a porous carbon material processed in a relatively simple three-dimensional shape, such as a bolt or a nut. However, this composite material has a lack of denseness and a rough surface which are characteristic of impregnation materials and also has a high cost. Therefore, the composite material is not used much in the present circumstances.
Furthermore, there has recently been developed a sintered C—SiC composite obtained by mixing ultrafine SiC powder having an average particle diameter of 10 to 100 nm and graphite particles and densifying the mixture to have a high density by spark plasma sintering (see Patent Literature 2). This composite material is reported to contain 1% to 95% by weight of SiC, have a relative density of 70% to 99.5%, and have a bending strength as high as 100 to 350 MPa. However, this composite material has a composite structure in which SiC particles and carbon particles are uniformly mixed, and does not rely on the concept that a composite material is formed to separate the interfaces between carbon particles through a ceramic. In addition, the type of ceramic used is limited to SiC.
Of carbon composite materials, C/C composites obtained by impregnating carbon fiber fabric with pitch and firing it and composite materials impregnated with resin are widely used. Although these composite materials have excellent strength, they do not achieve improved oxidation resistance and, therefore, the use of them in air at high temperatures is limited. In addition, these materials have rough surface, are difficult to process, and take a long time to be produced.